Plastic molding machines of carousel or turntable type generally include a linearly movable injection head having a plurality of molds carried on the turntable. The table is rotated in increments by an indexing mechanism and moved sequentially to locate a mold at a mold injection station. At the mold injection station the injection head is moved into and out of operative engagement with the mold. Control means responsive to the filling of a mold actuates the indexing mechanism and the injection head. In this type of machine appreciable difficulty is encountered in the precision requirements of machining and assembling the indexing mechanism to accurately locate a mold at the injection station for operative engagement with the injection head and of providing a locking mechanism that will lock the mold in such a position when the indexing mechanism is disengaged from the turntable.
Thus, in U.S. Pat. No. 3,327,354 intermittent rotation of the table to sequentially align the molds with the injection head is provided by means of a mechanical linkage adapted to releasably engage any of a plurality of indexing pins extended from the table and corresponding in number to the molds. The pins are also engageable by a locking mechanism which includes a bifurcated locking member movable into a straddling relation with a pin at the mold injection station.
A gear type indexing mechanism for a mold turntable is disclosed in U.S. Pat. No. 3,621,533. For each intermittent rotation of the table a pitch advancement of a drive gear must be made through an angle equal to 360.degree./14, to provide fourteen stops for each revolution of the table. The indexing mechanism functions to hold the table at an indexed position.
The molding machine of U.S. Pat. No. 3,314,112 has an indexing mechanism which includes a swing arm having a wedge plate engageable with pins on a turntable to provide table rotation. An indexed position is defined by a spring pressed ball that drops into a recess on the table each time the table rotates through the proper arc increment.
In U.S. Pat. No. 3,413,682, the rotational speed of the table is progressively reduced so that at a molding station the rotational speed is substantially zero. The mold alignment means is arranged to operate when the rotation of the table is stopped or its speed is substantially zero so as to eliminate excessive wear on the indexing mechanism and alignment means.